Signal-correlating apparatus for improving the angular resolution of a directionally ranging system

ABSTRACT

Means for improving the azimuth resolution of an azimuthally scanning ground-mapping radar. The sampled-and-held video for a given range bin is processed by a correlation filter having a preselected impulse response and then differentiated. A negativegoing zero level of the differentiated signal is employed as indicative of the scan time or angular position of the centroid of a sensed target to within less than the angular beamwidth of the antenna.

United States Patent [191 Ashcraft 51 Jan. 9, 1973 [54] SIGNALC()RRELATING APPARATUS 3.660.842 5/1972 Ballantyne ..343/16 R FORIMPROVING H ANGULAR 2,709,805 5/1955 Dodington ..343/16 RESOLUTION OF ADIRECTIONALLY P E T H T bb nmary xammer U esmg AttorneyL. Lee Humphries,H.. Fredrick Hamann [75] Inventor: William D. Ashcraft, Fullerton, and R|fM pin Calif.

[73] Assignee: North American Rockwell Corpora- [57] ABSTRACT tion, ElSegundo, Calif. Means for improving the azimuth resolution of an 22Filed; No 7 1969 azimuthally scanning ground-mapping radar. Thesampled-and-held video for a given range bin is processed [211 App!877311 by a correlation filter having a preselected impulse response andthen differentiated. A negative-going 52 us. Cl. ..343/7 A, 343/16 Rzero level of the differentiated signal is p y as [51] Int. Cl ..G01s9/02 indicative f h scan i or ng lar po i ion f he [58] Field of Search..343/7 A, 16 R n r i f a en e arget to wi hin le h n the angularbeamwidth of the antenna. 56 R f C't d I 1 e erences I e 15 Claims, 5Drawing Figures UNITED STATES PATENTS 3,077,595 2/1963 Frost ..343/16 RX SAMPllE VIDEO CORRELATING DERWATWE ZERO 8i HOLD CIRCUIT FILTER TAKINGcnossms AMPLIFIER DETECTOR RANGE GATE TRIGGER ONE SHOT MULTIVIBRATOR(500 sec) 35 GATE CONTROL TRA 3w VIDEO VIDEO "*OUTPUT "PUFIER TO msmvINDICATOR (OR OTHER 36 unuzmou DEVICE) PAIENIED JAN 9 1975 RADAR SYSTEMSHEET l I]? 3 FIG. I

INPUT FROM RANGE GATE RECEIVER SAMPLING FILTER HAVING IMPULSE FUNCTIONIIII W(T) 39" FIG. 2

RESPONSIVE TO A PRESELECT ED SENSE OF OUTPUT AMPLITUDE RATE OF CHANGE OFSAMPLING FILTER DISPLAY INDICATOR OR OTHER GATED SIGNAL UTILIZATIONMEANS INVENTOR. WILLIAM D. ASHCRAFT ATTORNEY PATENTEDJAN 9197s 3.710.384

SHEET 2 BF 3 SAMPLE VIDEO 8 HOLD ORRELATIN DERIVATIVE ZERO ClRCUlTFILTER TAKING cnossms AMPLIFIER DETECTOR RANGE GATE TRIGGER (500 1. sec)CONTROL TRANSISTOR SWHCH VIDEO VDE0 OUTPUT AMPUFIER m DQSPLAY INDICATORl 8 (OR OTHER 36 UTILflZATQOM DEVICE) FIG. 3

INVENTOR. WILLIAM D. ASHCRAFT ATTORNEY PATENTEDJAN 91973 3, 7 l O. 384

SHEET 3 [IF 3 'o '1 '2' s '4 '5 's '7 'a 'e '1 's '5 '4 '5 '2 'l '0 .92.i I I I I l f i I FIG. 4

IN VENTOR. WILLIAM D. ABHCRAFT ATTORNEY CROSS REFERENCE TO CO-PENDINGAPPLICATIONS l. U.S. application Ser. No. 686,113 filed Nov. 28, 1967 byC. L. Vehrs, Jr., for A Time Domain Correlator for Spatial Filtering ina Pulsed Energy System.

2. U.S. application Ser. No. 827,194 filed May 23, 1969 by D. K. Waineofor Signal Injection Means for Avoiding Monopulse Anomalies in aMonopulse Array, now U.S. Pat. No. 3,618,092.

3. U.S. application Ser. No. 639,238 filed May 17, 1967 by J. A. Moultonfor Range-Gated Moving Target Signal Processor.

4. U.S. application Ser. No. 799,038 filed Feb. 13, 1969 by C. L. Lutesfor Non-Linear Low Pass Filter, now U.S. Pat. No. 3,596,192.

BACKGROUND OF THE INVENTION In the utilization of adirectionally-ranging sensor such as a mapping radar or otherdata-sampling system for reconstructing a data matrix from the sampledelements thereof, the quality of the reconstructed image is a functionof the system resolution. In an azimuthally scanning pulse-type radar ina mapping application, for example, the radial resolution may bedetermined by the time-bandwidth product (which varies with thetransmitted pulsewidth), while the angular resolution tends to vary withthe angular beamwidth of the antenna response pattern. Substantialimprovement in radial or range resolution performance has beendemonstrated by means of the apparatus described in copending U.S.application Ser. No. 686,113 for A Time Domain Correlator for SpatialFiltering in a Pulsed Energy System, filed Nov. 28, I967 by C. L.Vehrs,.lr., assignor to North American Rockwell Corporation, assignee ofthe subject invention. However, the utility of such improvedrange-resolution improvement tends to be limited without correspondingimprovement in the angular resolution of the system.

Prior-art approaches to angular resolution improvement over thatinherent in the antenna beamwidth of the scanning antenna have includedmonopulse beamsharpening and monopulse on-boresight processingtechniques, as described, for example, in U.S. Pat. No. 3,283,322 issuedto R. E. Hovda et al for Monopulse Receiver Apparatus and a copendingU.S. application Ser. No. 827,194 for Signal Injection Means forAvoiding Monopulse Anomalies in a Monopulse Array filed May 23, 1969 byDouglas A. Waineo, assignor to North American Rockwell Corporation,assignee of the subject invention. Such monopulse resolution improvement (MRI) techniques are of limited utility in providing typically onlyabout a 2:1 resolution improvement, and further suffer from thedisadvantage that such pulse-to-pulse or single-pulse processing issubject to low signal-to-noise ratios. In other words, the receivedsignal and noise of only a single pulse repetition interval(representing an on-boresight condition) is employed in generating thedisplay signal for such repetition interval. Further, the utilization ofsuch techniques require care in the design of the associated antenna inorder to avoid monopulse anomalies due to certain sidelobe responseeffects as is described more fully in U.S. Pat. No. 3,355,738 issued toJ. A. Algeo for Microwave Antenna Having a Controlled PhaseDistribution.

Another prior-art technique for improving the angular resolution of aradar system over the beamwidth thereof, is described in U.S. Pat. No.2,803,819 to W. R. Blair for Object Locating System and involves themethod of manually or otherwise selectively scanning or oscillating anantenna over a narrow field of view of interest containing a target ofinterest and observing (on a display indicator) that bearing at whichthe target signal level is strongest or at which a maximum display levelis obtained. Such technique, obviously, is unsuited for use in anautomatic mapping display application for a radar system. The humanjudgment involved makes the result uncertain. Also, the delays involvedmake such a technique unacceptable where a high data rate system isrequired, as in an airborne mapping system.

SUMMARY OF THE INVENTION By means of the concept of the subjectinvention, the above-noted disadvantages and shortcomings of the priorart are avoided and a much improved angular resolution is provided andwhich is useful in a high data-rate mapping application.

In a preferred embodiment of the inventive concept, a range-gatedreceived signal sample [(t T) from a scanning sensor system iscorrelated with a replica or analog of the sensor angular pattern, andthe scanning direction associated with a maximum correlation isdetermined as the direction angle of interest. There is provided acorrelation filter responsive to a rangegated output of the system andhaving an impulse response W( T) corresponding to an analog ofanormalized replica of the response of the scanned sensor system to apoint source target.

Gating means, responsively coupled to the filter, interconnects receivedsignal utilization means (such as the intensity control of a PP] displayindicator) to the range-gated system output only during a preselectedchange in sense of the amplitude rate of response of the filter.

in normal operation of the above-described arrangement, the outputresponse of the correlation filter to the sampled input thereto isindicative of the function 1(t T) W( T)dT or correlation integral, thelook angle associated with the occurrence of the maximum value of thecorrelation integral corresponding to the true direction of the pointsource target. The resolution improvement so obtainable can be as highas :1, while the number of pulse repetition intervals or data samplesover which the data for a given point source target is correlatedresults in a substantial improvement in signal-to-noise performance.Further, no special design requirements are imposed on the antennasidelobe response.

Accordingly, it is an object of the invention to provide correlationmeans for improving the angular resolution of analog directional sensor.

It is another object of the invention to correlate the response of adirectional sensor with an analog normalized sensor response to morenearly determine the directional coincidence of a point source targetand the centroid of the directional response pattern of the sensor.

A further object of the invention is to provide directional sensorangular resolution improvement means providing enchanced signal-to-noiseratio performance, without imposing undue restraints upon the sensordesign.

These and-other objects of the invention will become more fully apparentfrom the following description, taken together with the accompanyingdrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a representation of thegeometry of the I problem solved by means of the invention;

FIG. 2 is a block diagram of a system embodying the concept of theinvention;

FIG. 3 is a block diagram of an exemplary embodiment of the system ofFIG. 2;

FIG. 4 is an exemplary weighting function response of the filter of FIG.2; and

FIG. 5 is a family of time histories of the response of the correlationfilter of FIG. 2, illustrating the manner of cooperation thereofinthesystem of FIG. 2. 7

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, thereis illustrated a representation of the geometry of the problem solved bymeans of the concept of the invention. There is illustrated a position10 of a directional sensor such as an azimuthally scanning radar,relative to which a point source target 11 is situated, the target asviewed from position 10 being of a radial extent much less than that(AR) represented by a transmitted pulsewidth and having an azimuthalextent much less than that (Adi) of the beamwidth of the sensordirective beam pattern 12. As

shown in FIG. 1, target 11 is lying on the boresight or centroid axis 13of beam pattern 12. However, a position anywhere within the beamwidthAd: of pattern 12 could not, without special processing, bedistinguished from that of target 11 on boresight axis 13. Similarly,

where the boresight axis of the directive beam pattern is scanned fromleft to right in FIG. 1, a boresight axis direction 14 for which theright edge of the beam pattern illuminates target 11 and anotherboresight axis direction 15 for which the left edge of the beam patternilluminates target 11 results in display indicator data erroneouslyindicating that the point source target has an angular extent, Ad),corresponding to the sensor beamwidth.

The displayed radial extent of target 11 may be substantially reducedfrom that (AR) corresponding to the transmitted pulsewidth by pulsecompression techniques and the like. By means of the concept of thesubject invention, the displayed azimuthal extent of target 11 issubstantially reduced from that (Ada) corresponding to the beamwidth ofsensor pattern 12 by the conceptual arrangement illustrated in FIG. 2.

Referring now to FIG. 2, there is illustrated in block form a systemembodying the concept of the invention. There is provided a directionalsensor system 16 such as, for example, a pulse type ranging system orradar providing a range-gated receiver output [(t). There is alsoprovided sampling filter means 17 for sampling the output of sensorsystem 16 and having a'preselected impulse function W( T). The impulsefunction W( T) of filter 17 is preselected as an analog of a normalizedreplica of the response of the scanning sensor or antenna to a pointsource of a pre'selectedor normal signal strength (as measured at theantenna). For example, for the antenna azimuthal beam pattern andantenna azimuthal scan rate for a given radar system 16, a normalizedreplica of the system response to a scanned point source target (ofnormal strength) may resenble the shape of :urve W( T) in FIG. 4, theskirts of the curve corresponding to the weak response of the beampattern edge in encountering the target, the peak of the curvecorresponding to the centroid or boresight axis of the beam, and thetime interval between the skirts corresponding to the like scan intervalof illumination provided by the ratio of the antenna beamwidth to theantenna scan rate. The design of an R-C network or filter to provide apreselected response, such as the representative impulse response, iswell understood in the art.

The response C(t) of filter means 17 at any point in time (t) to anapplied input [(13) from the range-gated receiver of radar system 16 isthe convolution integral of the filter impulse response W( T) and thetime history 1(t T) of such applied input signal. The variation in theenvelope corresponds to the variation in the antenna beam patternresponse as a function of target direction, relative to theboresightaxis, as the beam'pattern scans across the target, the function1(t) progressively varying from a weak signal sample (corresponding totarget illumination when the beam center is to one side 14 of the'target11 as shown in FIG. 1) to a subsequent maximum signal sample(corresponding to the beam pattern boresight axis 13 lying on the target11 in FIG. 1) and then decreasing to a weak signal sample (correspondingto target illumination when the beam center is to the other side 15 oftarget 11 as shown in FIG. 1). In otherwords, the shape of the envelopeof I(t for a point source target is similar to that of W( T), but willvary in amplitude scaling with variations in the strength of thereceived signal therefrom.

The response of filter 17 to a single impulse I( t,) may be describedfor any point in time (t, T,,) subsequent to the application of suchimpulse, as 1(t,)W( T Alter natively, the impulse response of filter 17at any given point in time (t) may be described as a function of aprior-applied impulse 1(t T,,) as 1(1- T,,) W( T,,). For

example, the subsequent response of filter 17 to the range-gatedreceiver output I(t,) occurring at t,, is shown as curve 21 in FIG. 5c.The response of filter 17 at a selected subsequent point in time, t t, Tto such prior applied input 1(t T is I(r T,)W(T,),

shown as element 41 in FIG. 5c. The subsequent response of filter 17 tothe range-gated receiver output I(t occurring at 1 is shown as curve 22in FIG. 5d, the responses to the remaining sampled inputs I(t I( t-,) ofFIG. 50 being similarly shown as curves 23-27 in FIGS. 5e-5i,respectively, the component response of filter 17 at the preselectedtime t to each of the applied inputs I(t I(t,,) being shown as elements43-47 respectively.

The actual output response C(t) of filter 17 at a preselected point intime, t, is, of course, the sum of the component responses at such pointin time to each of the prior applied impulse inputs thereto:

Such response, shown as element 28 of the locus 29 in FIG. 5h, is alsoknown as the convolution integral,

C(1t)=f; 104 W(T,,)dT

T t The function C(t) is seen to vary with time t, demonstrating amaximum at time t in FIG. 5j. Such maxima is manifested by a change insense of C(t), the rate of change of C(t), from a positive to a negativesense; and is observed to occur (curve 40 in FIG. 5k) slightly laterlater (A1,) than the occurrence of a maximum value of 1m), as to beindicative of the past direction coincidence of the beam centroid 13 andtarget 11 in FIG. 1. In other words, the occurrence of a maximum valueof the convolution integral represents the optimum correlation of thesystem response replica and the actual response to a point sourcetarget, corresponding to a delayed indication of that scan time (2associated with the direction angle (t.,)) of such point source target.

Signal gating means 18, responsive to such preselected change in senseof the rate of change of the output C(t) of filter 17 (in FIG. 2), maythen be employed to gatingly couple the input of signal utilizationmeans 39 to the range-gated system only during a scan time intervalcorresponding to the brief occurrence of the maxima, C as to provide adisplay of improved angular resolution. In other words, the cooperationof the correlating filter 17 in FIG. 2 collapses a point target displayin azimuth to a small fraction of the antenna beamwidth, so that thetarget appears as a point on the display. The true shape of a displayedtarget complex is thus more clearly perceived, general intepretation ofa ground map image is enhanced and the true azimuth position of a targetof interest may be more accurately determined.

As shown in the arrangement of FIG. 2, signal utilization means 39 iscoupled via gating means 18 to the range-gated, time averaged orintegrated output of filter 17. The advantage of such arrangement isthat such display signal, derived from received signals over a pluralityof pulse repetition intervals, is less noisy, the noise tending toaverage out over the integration interval, whereby an improvedsignal-to-noise ratio is obtained. Also, hard targets tend to stand outmore clearly on the display as to be more readily identifiable at longerranges. The constant delay Ai merely results in a small angular bias inthe rotation of the ground map display provided by utilization means 39.I

An exemplary mechanization of the. correlator arrangement of FIG. 2 isshown in fuller detail in FIG. 3. There is provided correlating filtermeans comprising range-gated sample-and-hold means 31 adapted to beresponsive to a receiver output of radar system 16 (of FIG. 2) andafilter circuit 32 responsive to sample-andhold means 31 and having apreselected impulse function corresponding to that described inconnection with FIG. 4. The construction and arrangement of a rangegatedsample and-hold means 31 is well understood in the art, as indicated bycopending U. S. application Ser. Nos. 639,238 filed May 17, 1967 forRange-Gated Moving Target Signal Processor by J. A. Moulton and 799,038filed Feb. 13, 1969 for Non-Linear Low Pass Filter by C. L. Lutes, bothof which applications are assigned to North American RockwellCorporation, assignee of the subject application; therefore, suchelement is shown in block form only. Filter 32 may be fashioned from asuitable RC network.

There is also provided in FIG. 3 rate signalling means 33 responsive toan output of filter circuit 32 for providing a signal indicative of theamplitude rate of change of the output of filter circuit 32. Such ratesignalling means may be comprised of a differentiating amplifierproviding impedance isolation as well as amplitude-rate signalling.There is further provided gate control means, coupled to an output ofrate-signalling means 33 and responsive to a preselected change of senseof the rate of change signal, for generating a gate control signal. Suchgate control means comprises a zero-crossing detector 34 for detectionof a rate signal change in sense indicative of the occurrence of acorrelation maxima (i.e., peak of curve 29 in FIG. 51'). An output ofdetector 34, indicative of such state, is fed to a one-shotmultivibrator 35 for generation of a gatecontrol signal (Curve 40 inFIG. 5k). Signal gate means 18, such as a switching transistor, having acontrol input responsive to the gate control signal, couples theintegrated output of filter 32 to a video amplifier 36 for providingboth impedance isolation and amplification of .the gated filter output,if desired.

Although the rate-signalling andl gate-control means of FIG. 3 have beendescribed in terms of conventional analog signalling components, it isclear that the concept of the invention is not so limited and thatequivalent digital signalling means :may be alternatively employed.Also, although the utilization of the inven tive concept has beendescribed in terms of improved angular resolution for a mapping radar,it is clear that the disclosed technique for angular resolutionimprovement may be applied to other types of ranging systems andscanning sensor systems. Further, the applicability of the concept isnot limited to only a single range-bin of a range gated system, but isto be understood as equally applicable to all range-bins of interest ina range-gated directionally ranging system. Moreover, the correlationconcept is not limited to range-gated systems, but is useful in adirectionally scanning, passive directional sensor to more accuratelydetermine the direction of an active point source target such as abeacon.

In other words, the correlation concept of the invention, is useful inany data pattern samplingsystem for improving the indicated directionalresolution thereof by correlating the actual system response with anormalized replica of the system response to a scanned point source dataelement, by means of a filter having an impulse response representing ananalog of such replica.

Although the invention has been described and illustrated in detail, itis clearly understood that the same is by way of illustration only andis not to be taken by way of limitation the spirit and scope of thisinvention being limited only by the terms of the appended claims. Iclaim: l. A method for improving the indicated directional resolution ofa range-gated directionally scanned directionally ranging system havingreceived signal utilization means and comprising the steps of subjectinga range-time gated sample-and-held electrical output of said system,indicative of a preselected target range, to a filter circuit having apreselected impulse function corresponding to an analog of a normalizedreplica of the response of said system to a scanned point source target;and

responsively coupling said signal utilization means to the output ofsaid filter circuit only during an interval of a rate of change ofsaidoutput of said filter indicative ofa maxima thereof.

2. In a data pattern sampling system having output signal utilizationmeans, correlation means for improving the indicated directionalresolution of said system and comprising signal shaping means responsiveto a range-gated output of said system and having an impulse responsecorresponding to an analog of a normalized replica of the response ofsaid sampling system to a point source data element; and

gating means responsively coupled to said signal shaping means forcoupling an input of said signal utilization means to said system onlyduring a preselected change in sense of the amplitude rate of responseof said signal shaping means corresponding to a maximum correlation ofsaid system response with said data element.

3. Means for improving the angular resolution of a directionallyscannable directional senso'r having a given beamwidth, comprisingcorrelating electrical filter means adapted to be responsively coupledto an electrical output of said sensor and having an impulse responsefunction corresponding to an analog of anormalized replica of thescanned sensor response to a point source target; and I meansresponsively coupled to said correlating filter for gating-on an outputthereof only during a preselected change in sense of the amplitude rateof response of said filter.

4. The device of claim 3 in which said filter means comprises grange-time-gated sample-and-hold means adapted to be responsive to anelectrical output of said sensor which is indicative of a preselectedtarget range; and v a filter circuit responsive to said sample-and-holdmeans and having a preselected impulse function.

5. The device of claim 3 in which said means for gating-on comprises 6.scanned directionally ranging system having received signal.

utilization means, means for improving the indicated directionalresolution of said system and comprising a correlation filter responsiveto a range-gated output of said system and having an impulse responsecorresponding to an analog of a normalized replica of the response ofsaid scanned system to a point source target; and gating meansresponsively coupled to said correlation filter for coupling said signalutilization means to said range-gated system output only during apreselected change in sense of the amplitude rate of response of saidfilter.

7. The device of claim 6 in which said signal utilization means isresponsively coupled to said system by said correlation filter and saidgating means in tandem.

8. The device of claim 6 in which said gating'means comprises a signalgate gatingly interconnecting an input of said signal utilization meansand an output of said filter and having a gate control input responsiveto a preselected change in sense in the amplitude rate of change of theoutput of said filter.

9. The device of claim 6 in which said gating means comprises i controlsignal means responsive to an output of said filter for providing acontrol signal only during a preselected change in sense of theamplitude rate of response of said output of said filter; and

a signal gate interconnecting an output of said signal utilization meansand saidoutput of said filter and having a gate control input responsiveto said controlsignal.

10. The device of claim 6 in which said filter means comprisesrange-time gated sample-and-hold means adapted to be responsive to anelectrical output of said sensor indicative of a-preselected targetrange;

a filter circuit responsive to 'said sample-and-hold means and having apreselected impulse function.

11. The device of claim 6 in which said means for gating-on comprisesrate-signalling means responsive to an output of said filter means forproviding aisignal indicative of the rate of change of said output ofsaid filter means gate control means responsive to an output of saidrate-signalling means responsive to a preselected change of sense ofsaid rate of change signal for generating a gate control signal; signalgate means coupled to said output of said filter and having a gatecontrol input responsive to said gate control signal.

12. In a directionally scanned directionally ranging system havingoutput signal-utilization means, correlation means for improving theindicated directional resolution of said system and comprisingrange-gated signal shaping means responsive to an output of said systemand having an impulse response corresponding to analog of a normalizedreplica of the response of said ranging system to a point source target;and gating means responsively coupled to said signal shaping means forcoupling said signal utilization means to said system only during apreselected change in sense of the amplitude rate of response of saidsignal means corresponding to a maximum correlation of said systemresponse with said point source target. v 13. A correlation techniquefor improving the indicated directional resolution of a data patternsampling system having output utilization means and comprising the stepsof subjecting a range-gated output of said system to signal shapingmeans having an impulse responsive corresponding to an analog of anormalized replica of the response of said sampling system to a scannedpoint source data element; and responsively coupling said signalutilization means to said system only during a preselected change insense of the amplitude rate of the response of said signal shaping meanscorresponding to a maximum correlation of said system response with saiddata element. 14. A correlation technique for improving the indicateddirectional resolution a data pattern sampling system having outpututilization means of and comprising the steps of subjecting arange-gated output of said system to signal shaping means having animpulse response corresponding to an analog ofa normalized replica ofthe response of said sampling system to a directionally scanned pointsource data element; and

responsively coupling said signal utilization means to said signalshaping means only during a preselected change in sense of the amplituderate of the response of said signal shaping means corresponding to amaximum correlation of said system response with said data element.

15. In a range-gated directionally scanned directionally ranging systemhaving received signal utilization means, means for improving theindicated directional resolution of said system and comprisingrange-time gated sample-and-hold means adapted to be responsive to anelectrical output of said system indicative of a preselected targetrange; a filter circuit responsive to said sample-and-hold means andhaving a preselected impulse function;

rate-signalling means responsive to an output of said filter means forproviding a signal indicative of the rate of change of said output ofsaid filter means;

gate control means coupled to an output of said ratesignalling means andresponsive to a preselected change of sense of said rate of changesignal for generating a gate control signal; and

signal gate means coupled to said output of said filter and having agate control input responsive to said gate control signal.

1. A method for improving the indicated directional resolution of arange-gated directionally scanned directionally ranging system havingreceived signal utilization means and comprising the steps of subjectinga range-time gated sample-and-held electrical output of said system,indicative of a preselected target range, to a filter circuit having apreselected impulse function corresponding to an analog of a normalizedreplica of the response of said system to a scanned point source target;and responsively coupling said signal utilization means to the output ofsaid filter circuit only during an interval of a rate of change of saidoutput of said filter indicative of a maxima thereof.
 2. In a datapattern sampling system having output signal utilization means,correlation means for improving the indicated directional resolution ofsaid system and comprising signal shaping means responsive to arange-gated output of said system and having an impulse responsecorresponding to an analog of a normalized replica of the response ofsaid sampling system to a point source data element; and gating meansresponsively coupled to said signal shaping means for coupling an inputof said signal utilization means to said system only during apreselected change in sense of the amplitude rate of response of saidsignal shaping means corresponding to a maximum correlation of saidsystem response with said data element.
 3. Means for improving theangular resolution of a directionally scannable directional sensorhaving a given beamwidth, comprising correlating electrical filter meansadapted to be responsively coupled to an electrical output of saidsensor and having an impulse response funcTion corresponding to ananalog of a normalized replica of the scanned sensor response to a pointsource target; and means responsively coupled to said correlating filterfor gating-on an output thereof only during a preselected change insense of the amplitude rate of response of said filter.
 4. The device ofclaim 3 in which said filter means comprises range-time-gatedsample-and-hold means adapted to be responsive to an electrical outputof said sensor which is indicative of a preselected target range; and afilter circuit responsive to said sample-and-hold means and having apreselected impulse function.
 5. The device of claim 3 in which saidmeans for gating-on comprises rate-signalling means responsive to anoutput of said filter means for providing a signal indicative of therate of change of said output of said filter means; gate control meanscoupled to an output of said rate-signalling means and responsive to apreselected change of sense of said rate of change signal for generatinga gate control signal; and signal gate means coupled to said output ofsaid filter and having a gate control input responsive to said gatecontrol signal.
 6. In a range-gated directionally scanned directionallyranging system having received signal utilization means, means forimproving the indicated directional resolution of said system andcomprising a correlation filter responsive to a range-gated output ofsaid system and having an impulse response corresponding to an analog ofa normalized replica of the response of said scanned system to a pointsource target; and gating means responsively coupled to said correlationfilter for coupling said signal utilization means to said range-gatedsystem output only during a preselected change in sense of the amplituderate of response of said filter.
 7. The device of claim 6 in which saidsignal utilization means is responsively coupled to said system by saidcorrelation filter and said gating means in tandem.
 8. The device ofclaim 6 in which said gating means comprises a signal gate gatinglyinterconnecting an input of said signal utilization means and an outputof said filter and having a gate control input responsive to apreselected change in sense in the amplitude rate of change of theoutput of said filter.
 9. The device of claim 6 in which said gatingmeans comprises control signal means responsive to an output of saidfilter for providing a control signal only during a preselected changein sense of the amplitude rate of response of said output of saidfilter; and a signal gate interconnecting an output of said signalutilization means and said output of said filter and having a gatecontrol input responsive to said control signal.
 10. The device of claim6 in which said filter means comprises range-time gated sample-and-holdmeans adapted to be responsive to an electrical output of said sensorindicative of a preselected target range; a filter circuit responsive tosaid sample-and-hold means and having a preselected impulse function.11. The device of claim 6 in which said means for gating-on comprisesrate-signalling means responsive to an output of said filter means forproviding a signal indicative of the rate of change of said output ofsaid filter means gate control means responsive to an output of saidrate-signalling means responsive to a preselected change of sense ofsaid rate of change signal for generating a gate control signal; signalgate means coupled to said output of said filter and having a gatecontrol input responsive to said gate control signal.
 12. In adirectionally scanned directionally ranging system having output signalutilization means, correlation means for improving the indicateddirectional resolution of said system and comprising range-gated signalshaping means responsive to an output of said system and having animpulse response corresponding to analog of a normalized replica of theresponse of said ranging system to a point source target; and gatingmeans responsively coupled to said signal shaping means for couplingsaid signal utilization means to said system only during a preselectedchange in sense of the amplitude rate of response of said signal meanscorresponding to a maximum correlation of said system response with saidpoint source target.
 13. A correlation technique for improving theindicated directional resolution of a data pattern sampling systemhaving output utilization means and comprising the steps of subjecting arange-gated output of said system to signal shaping means having animpulse responsive corresponding to an analog of a normalized replica ofthe response of said sampling system to a scanned point source dataelement; and responsively coupling said signal utilization means to saidsystem only during a preselected change in sense of the amplitude rateof the response of said signal shaping means corresponding to a maximumcorrelation of said system response with said data element.
 14. Acorrelation technique for improving the indicated directional resolutiona data pattern sampling system having output utilization means of andcomprising the steps of subjecting a range-gated output of said systemto signal shaping means having an impulse response corresponding to ananalog of a normalized replica of the response of said sampling systemto a directionally scanned point source data element; and responsivelycoupling said signal utilization means to said signal shaping means onlyduring a preselected change in sense of the amplitude rate of theresponse of said signal shaping means corresponding to a maximumcorrelation of said system response with said data element.
 15. In arange-gated directionally scanned directionally ranging system havingreceived signal utilization means, means for improving the indicateddirectional resolution of said system and comprising range-time gatedsample-and-hold means adapted to be responsive to an electrical outputof said system indicative of a preselected target range; a filtercircuit responsive to said sample-and-hold means and having apreselected impulse function; rate-signalling means responsive to anoutput of said filter means for providing a signal indicative of therate of change of said output of said filter means; gate control meanscoupled to an output of said rate-signalling means and responsive to apreselected change of sense of said rate of change signal for generatinga gate control signal; and signal gate means coupled to said output ofsaid filter and having a gate control input responsive to said gatecontrol signal.